Re: [PATCH net] net: wwan: t7xx: off-by-one error in t7xx_dpmaif_rx_buf_alloc()

[Sergey Ryazanov <ryazanov.s.a@gmail.com>]

Hello Jinjie,

On 28.10.2024 10:06, Jinjie Ruan wrote:
> The error path in t7xx_dpmaif_rx_buf_alloc(), free and unmap the already
> allocated and mapped skb in a loop, but the loop condition terminates when
> the index reaches zero, which fails to free the first allocated skb at
> index zero.
> 
> Check for >= 0 so that skb at index 0 is freed as well.

Nice catch! Still implementation needs some improvements, see below.

> 
> Fixes: d642b012df70 ("net: wwan: t7xx: Add data path interface")
> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
> ---
>   drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c b/drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c
> index 210d84c67ef9..f2298330e05b 100644
> --- a/drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c
> +++ b/drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c
> @@ -226,7 +226,7 @@ int t7xx_dpmaif_rx_buf_alloc(struct dpmaif_ctrl *dpmaif_ctrl,
>   	return 0;
>   
>   err_unmap_skbs:
> -	while (--i > 0)
> +	while (--i >= 0)
>   		t7xx_unmap_bat_skb(dpmaif_ctrl->dev, bat_req->bat_skb, i);

The index variable declared as unsigned so changing the condition alone 
will cause the endless loop. Can you change the variable type to signed 
as well?

--
Sergey